In the following, a wheel loader is described as a working vehicle. The engine of a wheel loader constitutes both a drive source for traveling and a drive source for working equipment. Namely, a vehicle travels as a result of engine output being transmitted to drive wheels via a torque converter. Further, various hydraulic pumps including hydraulic pumps for working equipment are driven by the engine. Various devices such as working equipment can then be driven via hydraulic actuators using the hydraulic pumps. Specifically, for example, a hydraulic oil pump for steering use is driven by the engine. Hydraulic oil emitted by the hydraulic pump for steering is then supplied to hydraulic cylinders for steering and a steering mechanism is driven. Further, a hydraulic loader pump is driven by the engine, hydraulic oil emitted from the hydraulic loader pump is supplied to a hydraulic loader cylinder and the loader is driven.
This wheel loader can use the output of a single engine in both driving for traveling and driving of various devices such as working equipment. The engine output that is capable of being used for traveling is therefore influenced by the size of the load on the working equipment.
For example, when the engine speed is a low idle speed (idling), the rise in engine torque with respect to an abrupt rise in hydraulic oil load slackens compared to when engine speed is high. However, when carrying out work where a high hydraulic load is suddenly applied such as when a loader lifts up a load while turning the steering wheel during idling, there are cases where it is difficult for the rise in engine torque to follow the abrupt rise in the hydraulic load and the engine therefore stops.
The engine output is also taken up by the working equipment and hydraulic loads for steering when the loader and the steering mechanism are operated while traveling. This means that it is only possible to use what remains of the engine output for the travel load. The response to accelerator operations by an operator therefore falls due to sufficient haulage power not being obtained or due to a long time being required to increase vehicle speed.
In the devices shown in Japanese utility model registration number 2514319 and Japanese Patent Publication Laid-open No. 10-219733, when the traveling side is subject to predetermined conditions, the pump capacity on the working equipment side is suppressed and the ability to travel is impeded.